JP2015-161225A discloses an intake and exhaust system of an engine in which an exhaust gas recirculation (EGR) passage which leads a portion of exhaust gas as an EGR gas from an exhaust passage located downstream of a DPF (Diesel Particulate Filter) to an intake passage is provided, and an EGR cooler and an EGR valve are provided in the EGR passage.
In the intake and exhaust system, the DPF is arranged on a rear side of an engine body with its axis extending in a lined-up direction of cylinders, and an exhaust pipe extending at the rear of an automobile is connected to a downstream end of the DPF. The EGR cooler is connected to a side surface (an opposite side from the DPF) of the exhaust pipe, and the EGR valve is fixed to a side surface (an opposite side from the DPF) of the EGR cooler. An EGR pipe extends upward from the EGR valve and is connected to a horizontally extending part of an intake pipe located upstream of a compressor of a turbocharger. Further, a blow-by gas pipe which introduces blow-by gas into the intake passage is connected to a position near a connected part of the intake pipe with the EGR pipe.
With this intake and exhaust system, the EGR gas horizontally passes through the EGR cooler from the exhaust pipe, and then is led upward from the EGR valve through the EGR pipe.
In the intake and exhaust system, when condensed water is generated in the EGR passage, the condensed water may stagnate in a horizontal part of the EGR passage, that is, in a part where the EGR cooler and the EGR valve are provided. In this regard, it may be considered to arrange the EGR passage, including the EGR cooler, to extend vertically from the exhaust passage to the intake passage. According to this structure, the condensed water is discharged to the exhaust passage through an EGR passage wall and is prevented from stagnating in an intermediate part of the EGR passage.
However, forming the EGR passage as such reduces a passage resistance when the EGR gas flows from the exhaust passage toward the intake passage. As a result, it becomes easy for the EGR gas to pass through the EGR cooler, which lowers cooling efficiency of the EGR gas by the EGR cooler. That is, it becomes more difficult to cool the EGR gas.